Field of the Invention
The present invention relates to a sheet bundle binding device that bundles a plurality of sheets fed from, e.g., an image forming device and automatically performs staple-free binding for the sheet bundle and an image forming system having the sheet bundle binding device.
Description of the Related Art
Recently, in addition to a stapling device that drives a metal needle into a plurality of stacked sheets to bind the sheets, there is used a staple-free binding device that sandwiches a plurality of stacked sheets between a pair of concavo-convex crimping teeth and strongly presses the sheets for pressure bonding to bind the sheets. Both the stapling device and the staple-free binding device have a problem in that when some sheets need to be removed from the bound sheet bundle, the removing operation is very troublesome, and all the sheets of the sheet bundle tend to be separated from each other.
To solve the above problem, there is proposed an image forming device provided with a stapler that drives a staple needle in a sheet bundle stored in a discharge tray and a sewing unit that forms perforation on the sheet bundle at a position surrounding a stable needle driving position. With this configuration, a desired sheet can be cut off along the perforation to be removed from the sheet bundle (see, for example, Patent Document 1). Further, there is known a sheet post-processing that unifies some small group sheet bundles bound by a staple needle driven inside a perforation into a large group sheet bundle and then binds the large group sheet bundle with a staple needle at an outside portion of the perforation. With this configuration, the small group sheet bundle can be cut off along the perforation and removed from the large group sheet bundle (see, for example, Patent Document 2).
In the staple-free binding, when the number of sheets to be bound is increased, a binding force between sheets constituting a sheet bundle is reduced, so that the number of sheets that can be bound in single binding processing is limited. In order to cope with this, there is known a sheet processing device that has a plurality of binding sections that perform staple-free binding for a sheet bundle at different binding positions, wherein a part of a sheet bundle bound at one binding position is bound together with another sheet bundle bound at another binding position so as to increase the number of sheets to be bound (see, for example, Patent Document 3).
Further, there is proposed a sheet bundle binding device provided with both a stapler unit that binds a sheet bundle by driving a staple needle into the sheet bundle and a staple-free binding unit that press-binds a sheet bundle without using a staple needle (see, for example, Patent Document 4 and Patent Document 5). A user can select the staple binding or staple-free binding according to the usage of the sheet bundle.